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66 DESIGN007 MAGAZINE I DECEMBER 2018 The smoke has not even cleared, but they already know what the problem is. It was supposed to be a celebratory moment for the team, plugging in the first board from the ini- tial shipment. Instead, the room is as silent as a morgue. The engineer steps forward to do the postmortem and immediately sees the issue. The integrated circuit (IC) has a pinhole melted into the surface, telling the story of the destruction within. This doesn't melt the part usually; it just quietly kills it and is more of a noise thing. They trace back along the board, and the decoupling capaci- tor is nowhere to be found. A completely predictable voltage spike overcame the fragile circuit. The engi- neer knows that they put the capacitor in place. However, on closer examination, it is not close enough to the IC pad to make a difference. Everyone turns to the PCB designer. "But I put it right where the schematic said to!" they say. The fix is easily implemented. It takes 15 minutes to produce a new design. Unfortu- nately, the break room already has an ample supply of coasters, and that's all this batch of boards can now be used for. The project will lose days and dollars. How did this confusion come about? Make Lovable Schematics When engineers start to put together projects, they are not just mak- ing circuits—they are writing a message to the PCB designer. Their work prod- uct—and thus, their process— needs to be a helpful part of a team effort. The schematic is, at first, the space in which an engineer does their thinking. However, by the time they hand it off to the designer, it needs to be a clean, comprehensible document that eliminates vagaries. In the nightmare scenario above, the designer ends up in the crosshairs, but what could the engineer have done to prevent the problem and save that first run of boards from Key Guidelines for Clean Schematic Designs Connect the Dots by Bob Tise and Dave Baker, SUNSTONE CIRCUITS

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